Gas silencing structure

ABSTRACT

An air gap conduit for exhaust gases of an internal combustion engine has openings located at high pressure points which connect the gas flow passage to the space between inner and outer layers of the pipe.

United States Patent [191 11] 3,780,826 Hubbell, III Dec. 25, 1973 GAS SILENCING STRUCTURE Prima Examiner-Richard B. Wilkinson 75 I t:F klR.Hbbll,I,B l, 1 men or f m u e H rook yn Assistant Examiner--V1t W. Mlska Attorney---Jv King Harness et al. [73] Assignee: Tenneco Inc., Racine, Wis.

[22] Filed: Aug. 9, 1972 [2]] Appl. No.: 279,245' ABSTRACT [52] 181/36 181/36 An air gap conduit for exhaust gases of an internal [51] Int Cl F01 3/06 combustion engine has openings located at high pres- [58] Fieid /36 B 48 sure points which connect the gas flow passage to the space between inner and outer layers of the pipe. [56] References Cited UNITED STATES PATENTS 1 Claim, 3 Drawing Figures 3,263,772 8/[966 Irwin et al. l8l/36 B 1 GAS SILENCING STRUCTURE BRIEF SUMMARY OF THE INVENTION It is the purpose of this invention to provide an exhaust gas silencing system of relatively small external size but which is capable of attenuating troublesome sound frequencies in the exhaust gases including relatively low sound frequencies.

The invention accomplishes this purpose by means of an air gap pipe, that is, a pipe comprising an inner conduit through which the gas flows and an outer concentric conduit which is spaced from the inner conduit and defines with it an annular air chamber extending along the lengths of the two conduits. Openings in the inner conduit at high pressure points (anti-nodes) of troublesome frequencies enable the chamber between the two pipes to be used for sound attenuation.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side elevation of an exhaust system embodying the invention, it being partly broken away and in section;

FIG. 2 is an enlarged view of the structure shown within the circle of FIG. 1; .and

FIG. 3 is a cross section through a modified form of the invention.

DETAILED DESCRIPTION OF THE INVENTION An internal combustion engine 1 has an exhaust manifold 3 which discharges exhaust gases into an exhaust system 5 that carries them to an outlet 7 from the exhaust system for discharge into the atmosphere. The exhaust system 5 is illustrated as a pair of concentric conduits 9 and 11 which are bent at various points as required to fit the space available beneath the frame of an automotive type vehicle. The inner conduit 9 provides a straight through flow passage 13 for exhaust gas to flow from the manifold 3 to the outlet 7. The annular space between the conduits 9 and 11 serves as an air gap or longitudinally extending chamber 15 that may be closed at both the inlet and outlet ends, as by necking down of the outer conduit in contact with the inner conduit as indicated at 17 and 19. In a typical installation the inner pipe 9 might be 2 inches in outer diameter, and the outer pipe 11 2% inches in outer diameter, leaving a fairly substantial width of chamber 15 between the two pipes.

In accordance with this invention, holes of a specific size and shape are formed in the inner pipe 9 at the high pressure points (anti-nodes) of sound frequencies that it is desired to attenuate. The number of holes will de pend on the tuning requirements for each individual frequency. The location and the diameter or total area or size of each hole is important and may be related to the volume of the chamber 15 so that a hole functions as a tuning neck and the space 15 as a resonator volume to enable tuning in accordance with the Helmholtz formula. Alternatively, tuning could be on the quarter wave or Quincke principle in which case the length of the chamber 15 connected to the hole should be about one quarter the wave length of the frequency to be attenuated.

To illustrate the invention, hole 21 may be about 1 inch in diameter, the hole 23 about 1% inches in diameter, and the hole 25 about 2 inches in diameter, the holes being located at high pressure points of the frequencies it is intended for them to attenuate. As the exhaust gas flows through the passage 13, high pressure pulses of gas of the tuned frequencies will be acoustically connected through the openings 21, 23, and 25 to the space 15 so that effective attenuation is achieved.

In the arrangement of FIG. 3, an inner pipe 51 (which corresponds to pipe 9) has a portion concentrically surrounded by an outer pipe 53 which is necked down at opposite ends 55 and 57 into contact with the inner pipe to thereby form an annular chamber 59 between the two pipes. .The two pipes may be of sizes corresponding to those indicated in FIG. 1 and the pipe 51 would provide an internal passage 61 for the flow of exhaust gas. The inner pipe 51 has an opening 63 which is sized in the manner indicated above and located at a pressure point in the exhaust system for the frequencies it is desired to attenuate by its connection with the chamber 59.

Modifications may be made without departing from the spirit and scope of the invention. If it is desired to use a muffler in the system it would be placed donwstream of the air gap pipe.

I claim:

1. In an exhaust gas system for an internal combustion engine having an exhaust manifold, an exhaust gas conduit connected to the manifold to convey gas therefrom, a tubular member surrounding substantially the entire length of the conduit and defining a sound attenuating chamber around the conduit extending along substantially the entire length of the conduit, said member being closed at opposite ends to close said chamber, said conduit having a plurality of openings therein connecting the interior of the conduit to said chamber, said openings being spaced lengthwise from each other in the conduit and located substantially at a plurality of high pressure points of sound frequencies to be attenu- 

1. In an exhaust gas system for an internal combustion engine having an exhaust manifold, an exhaust gas conduit connected to the manifold to convey gas therefrom, a tubular member surrounding substantially the entire length of the conduit and defining a sound attenuating chamber around the conduit extending along substantially the entire length of the conduit, said member being closed at opposite ends to close said chamber, said conduit having a plurality of openings therein connecting the interior of the conduit to said chamber, said openings being spaced lengthwise from each other in the conduit and located substantially at a plurality of high pressure points of sound frequencies to be attenuated. 